1. Field of the Invention
The present invention is directed to the field of electrical dimming controls and more specifically, to those controls associated with vehicular instrument panel illumination.
2. Description of the Prior Art
In the simplest configuration, vehicular panel dimming controls often include a manually adjustable variable resistor connected in series with an associated illuminating lamp load to supply a selected amount of voltage thereto. Some also include an on-off switch for supplying power to auxiliary loads such as reading or dome/interior lamps.
Other dimmer control configurations, such as that shown in U.S. Pat. No. 3,371,241, utilize pulse-width modulation circuitry to supply varying duty cycles to the controlled load, in accordance with the setting of a variable resistor.
In each of the prior art systems, the power supplied to the controlled load is substantially constant for each selectable resistance value. In a vehicle environment where a dimmer control is used to select the intensity of illumination on various instruments and gauges, numerous manual readjustments are required to maintain a comfortable contrast from the time the instrument illumination is turned on at dusk as opposed to later at night in complete darkness.